Ḥadīth al-thaqalayn (Arabic: حَديث الثَّقَلَين, literally: hadith of the two weighty things) is a famous and mutawatir (massively transmitted) hadith from the Prophet (s), which enjoins Muslims to follow the Qur'an and Ahl al-Bayt (a) after the Holy Prophet's (s) demise. Based on this hadith, Muslims should refer to the Qur'an and Ahl al-Bayt (a) and these two are inseparable.

The hadith is accepted by all Muslims, both Sunni and Shi'a, as authentic and has been recorded in the hadith collections of all Muslim sects.

Relying on this hadith, Shi'a scholars prove the necessity of the Imam, his infallibility, and the continuation of Imamate in all times.

"Indeed I am leaving two things among you, to which if you hold yourself, you will never astray: the book of Allah –who is all mighty and great- and my ahl al-bayt (household), my 'itra (family). O people hear! And I have announced to you that: indeed you will enter my presence and I will ask you about what you did to the thaqalayn (two weighty things) and the thaqalayn are the book of Allah and my ahl al-bayt."

"Looks like I have been called, and I answered (my time of death has come), indeed I have left the thaqalayn (two weighty things) among you, one of them is greater form the other, the book of Allah and my 'itra (family), my ahl al-bayt (household). So look after how you will behave with them after me, indeed they will never separate from each other until they enter my presence by the pool [in the paradise]."

Place and Time

There's disagreement about when and where the hadith is stated; for example Ibn Hajar al-Haytami says: "the Prophet (s), stated the hadith of thaqalayn, after the conquest of Mecca, on his way back to Medina, in Ta'if";[25] but others mentioned other times and places.

Studying these different hadiths, it's apparent that although some of them could be considered as different reports about a single occurrence, but not for many others; so it is clear that the Prophet (a) has mentioned the importance of thaqalayn (Qur'an and ahl al-bayt (a)) in different times and places, especially in his last days of life.[26]

The following are some of the places and times mentioned in historical reports:

In bed, when he was ill and some of the companions were around him.[36]

Sunna or 'Itra?

In some of the sources of Sunnis, instead of the word "'itra" (family) the word "sunna" (tradition) has been mentioned.[37] These narrations are rare and even Sunni scholars have not considered them; because the hadith with the word "sunna" has not appeared in earlier reliable sources.

Who are 'Itra?

In most of the narrations the phrase "ahl al-bayt" has come as a description for the word "'itra", but in some narrations only "'itra",[38] and in some other only "ahl al-bayt" has come,[39] and in some cases the order about the obedience of ahl al-bayt is repeated.[40]

Importance

Shi'a scholars have narrated the hadith of thaqalayn in their books and have referred to it as a proof for some of the Shi'a beliefs. Mir Hamid Husayn (d. 1306/1888) has dedicated a comprehensive chapter of his book 'Abaqat al-anwar to the hadith of thaqalayn and its chains of narrators based on Sunni sources. In the discussion of Imamate, he had mentioned this hadith prior to other related hadiths.

Some of the beliefs of Shi'a could be proved using hadith of thaqalayn:

Necessity of the Obedience of Ahl al-Bayt (a)

In the hadith of thaqalayn, ahl al-bayt (a) are put next to Qur'an, and this is stated that they will not separate from each other; therefore, as the obedience of the Qur'an is necessary for Muslims, so is the obedience of ahl al-bayt (a).

Infallibility of Ahl al-Bayt (a)

There are two points in hadith of thaqalayn about the infallibility of ahl al-bayt (a):

Putting stress on that if you obey the Qur'an and ahl al-bayt (a), you will never astray. This clearly shows that there's no error in the teachings of ahl al-bayt (a).

The companionship of ahl al-bayt (a) with Qur'an shows that as Qur'an is free from any error –according to the consensus (ijma') of Muslims- so the other side (ahl al-bayt (a)) must also be free from errors.

In addition to Shi'a scholars some Sunni scholars have also accepted the indication of the hadith to the infallibility of ahl al-bayt (a).[42]

Necessity of the Continuation of Imamate

The companionship of ahl al-bayt (a) with Qur'an shows that as Qur'an is the source of guidance in Islam, so there must always be someone from ahl al-bayt (a) to whom people refer in religious issues.

The Prophet (a) emphasizes that the Qur'an and ahl al-bayt (a) will never separate from each other.

The Prophet (a) says if you hold yourself to these two, you will never astray.

"It is realized from the hadith of thaqalayn that there is always a person from ahl al-bayt (a) who deserves to be followed, till the Day of Judgment; so he is meant by the persuasion in the hadith, as the book (Qur'an) is like this [which is and will be always available]."[44]

Scientific Authority of Ahl al-Bayt (a)

Since the Qur'an is the main source of beliefs and practical rulings of all Muslims and according to hadith of thaqalayn ahl al-bayt (a) are the inseparable company of the Qur'an, it is clear that ahl al-bayt (a) are the infallible scientific authority in all of Islamic sciences.

Hadith al-Thaqalayn and Proximity of Islamic Sects

As mentioned above, the hadith of thaqalayn is accepted by both Shi'a and Sunni scholars. There have been many discussions about the hadith which have resulted in the convergence of Islamic sects; including the discussion of Sayyid 'Abd al-Husayn Sharaf al-Din with al-Shyakh Sulaym al-Bushri, one of the Sunni scholars; the discussion formed the book al-Muraji'at.[46]